This invention relates to apparatus for maintaining a uniform grade of the surface being excavated or leveled by a waterborne dredge, and more particularly, to apparatus, including a laser beam--photo receiver system and a specially designed pulley arrangement, for compensating for water swell and other disturbances of waterborne dredges so as to maintain a uniform grade of the surface being excavated or leveled. Up and down movement of waterborne dredges caused by water swell or other disturbances is accentuated at the lower end of dredging ladders where the cutter action occurs. Water swell particularly effects cutters mounted on the end of barges and causes irregularities in the grade of the surface being dredged. Such irregularities may be enlarged because they interrupt streamline water flow and create localized water turbulence. Such localized water turbulence will cause scouring and depositing of sediment.
Various different mechanisms for water swell compensators in waterborne dredges and optic systems for controlling machines of the like are known in the art. Examples of such systems are disclosed in the following U.S. Pat. Nos.:
U.S. Pat. No. 2,289,242 to Chance et al discloses an optic system for controlling a motor. The system is particularly adopted for use in automatic steering systems for dirigible craft to maintain the craft on its course;
U.S. Pat. No. 2,926,437 to Ellicott, Jr. discloses a hydraulic system for raising and lowering the ladder of a waterborne dredge;
U.S. Pat. No. 3,343,810 to Parnell discloses a load compensation system that includes a hydraulic system to displace sheaves of pulleys to compensate for dynamic load changes;
U.S. Pat. No. 3,452,207 to Tuckerman discloses apparatus for controlling dredges and other machines. The apparatus includes a laser beam which provides a reference line;
U.S. Pat. No. 3,512,281 to Hadjidakis discloses apparatus for swell compensation in suction dredges. The apparatus of this invention includes activating switches on either side of a median position on a compensator plate. When the suction pipe loses contact with the riverbed, winchmotors are activated on the suction pipe suspension to make adjustments proportionate to the swell height;
U.S. Pat. No. 3,535,801 to Richter discloses hydraulic cylinders for raising and lowering the ladder of a waterborne dredge cutter;
U.S. Pat. No. 3,551,057 to Hamilton et al discloses apparatus for aligning large structures such as aircraft tooling jigs by means of a laser reference beam projected onto a light sensitive target;
U.S. Pat. No. 3,588,249 to Studebaker discloses surveying apparatus that includes a laser beam for establishing a survey reference plane;
U.S. Pat. No. 3,649,122 to Haltz discloses apparatus which includes a laser beam--photoelectric system for measuring coordinates and differences in terrain height relative to a reference point;
U.S. Pat. No. 3,734,564 to McKay et al discloses a dredge having swell compensating means that includes a block and tackle system that responds to sonic sensing means;
U.S. Pat. No. 3,777,376 to Treine et al discloses apparatus using hydraulic lift compensators which are actuated by pressure on the bucket or cutter from the floor;
Similarly, U.S. Pat. No. 3,797,139 to Larralde also discloses lift compensators that respond to the relative pressure on the bucket or cutter from the floor;
U.S. Pat. No. 3,893,249 to Wolters discloses dredging apparatus that uses a cable length varying lever to maintain constant pressure;
U.S. Pat. No. 3,948,486 to Jourdan et al discloses a hydraulic block and tackle system to compensate for movement caused by swells; and
U.S. Pat. No. 3,949,496 to de Koning et al discloses dredge apparatus that responds to cable pressure and provides a cable length variation to maintain constant pressure.
This invention represents an improvement over the prior art waterborne dredge compensator systems. The system of this invention responds very quickly to raise and lower the ladder in response to movement by the dredge and includes an A-frame, hydraulic lifter and a specifically designed block and tackle assembly for support and control of the cutter ladder to maintain the cutter at a constant elevation.